CWebUser, authentication

By default, the expression Yii::app()->user returns a [CWebUser] [application component](http://www.yiiframework.com/doc/guide/basics.application#application-component) which represents the information that are closely related with the current user. Some information can be persistent throughout the current user session. For example, [CWebUser] already comes with a [name|CWebUser::name] property that stores the username of the current user. In order to store more information, we need to modify the [identity|ICUserIdentity] class used together with [CWebUser]. Each application may have one or several identity classes which are mainly responsible to provide ways of performing user [authentication](http://www.yiiframework.com/doc/guide/topics.auth).

Here we use the `UserIdentity` class included in the `testdrive` application as an example, assuming our goal is to add the ID and the last login time of the user to [CWebUser]. We would modify `UserIdentity` as follows,


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